Outline

Objective: An optimal entry point for endoscopic procedures in the third ventricle is determined by anatomical landmarks like the foramen of Monroi, the floor of the third ventricle and the entrance to the Sylvian aqueduct. On a virtual basis retrospectively the individual borehole localisation for these procedures was determined.

Methods: In 42 children (20 boys; mean age: 6.2 Â± 5.9yrs) thin sliced T2 weighted MR-images (1.5T, Gyroscan, Philips) were analyzed within a 3D planning software (Brainlab cranial 2.5) to determine the trajectory to the floor of the third ventricle or the entrance to the Sylvian aqueduct. The crossing point at the skull convexity was determined as respective entry point to reach the targets. Coordinates are given relative to nasion and midline. In addition a mean trajectory was defined to reach both targets with minimal distortion of tissue margins at the foramen of Monroi. The results were compared to the real burr-hole localization used in the respective surgeries. Results are given as mean Â± SD.

Results: The entry point to reach the floor of the third ventricle or the Sylvian aqueduct measured 119 Â± 27.3mm / 21.0 Â± 11.8mm (distance from nasion/ distance from midline) and 55.3 Â± 26.5mm / 19 Â± 8.8mm, respectively. The virtual mean entry point to reach both targets was 85.3 Â± 26mm / 21.6 Â± 10mm. A high deviation of coordinates could be observed. Statistical differences in the sagittal coordinates of entry points were shown between of the trajectory reaching the Sylvian aqueduct, the mean trajectory and the borehole localization, which was actually used in these patients (p<0.01). The tissue shift at the level of the foramen of Monroi using the mean trajectory (4.5 Â± 2.4mm) were significantly lower compared with the trajectory of the burr-hole used in the patients to reach the Sylvian aqueduct (10.2 Â± 3.8mm; p<0.05).

Conclusions: Individualized planning of entry points for neuroendoscopic surgery is recommended, when targets are located in the posterior portions of the third ventricle. We suggest computer assisted planning to determine optimal trajectories.